The present invention relates to a method for the production of a board with printed circuit (printed circuit board) shielded against interfering radiation and having at least one electronic component.
It is customary for an electronic device to be protected, either in order to protect the electronic device itself against interfering radiation coming from an external source or in order to protect the environment against radiation generated by the electronic device itself.
Electronic devices which may be sensitive to interfering radiation, such as electromagnetic radiation, are electronic regulating, control and switching devices, and likewise communications equipment and data processing equipment, comprising one or more boards having a circuit on them and provided with electronic components, which circuit comprises a network of electrical conductors. Examples of such devices comprise, for example, microdata processors, computers, integrated circuits, microswitches, mobile telephones, transmitting and receiving equipment, pagers, television and so forth.
The term “shielding” is used in the art when referring to such protection of electronic equipment. The requirements which the abovementioned devices have to meet as regards such protection are becoming increasingly strict, and to an increasing extent are being laid down at international level.
Suitable shielding materials are generally composed of materials with good electrical and/or magnetic conducting properties, and are consequently often composed of metal. Examples of such shielding are metal casings or plastic coverings provided with a thin metal layer and generally applied to the inside of a housing. Various techniques are known for the application of such a metal layer directly to the inside of a housing or to a thin plastic film. Examples are metal painting, electroless plating, electroplating, vapour deposition and sputtering. In addition to these often complex, and therefore expensive techniques, in-mould foiling is a known process, in which either a metallized plastic film is deformed in a mould, for example by deep drawing, or a previously deformed metallized plastic film is placed in a mould, and in both cases a molten resin is subsequently poured into the mould, in order to place a carrier against the deformed metallized plastic film. Said carrier is often the housing or a part of the housing. This technique and the shielding materials used in it are described in, for example, WO99/40770 of the applicant.
EP-A-0,806,892 also discloses a production method, in which a shield is used, which shield consists of a plastic substrate which is first deformed and then metallized. Such a metallization of an already deformed plastic substrate is, however, difficult to carry out. The shield is fixed by means of conducting adhesive tape to an earth track of a board with printed circuit.
Although some of the abovementioned techniques provide good shielding results, there is a need among manufacturers of the abovementioned electronic equipment for simple shielding techniques, in particular for techniques that can be used by the manufacturer himself during the assembly of the electronic equipment.